1. Field of the Invention
The present invention relates to the field of three-way valves, and fuel injectors using three-way valves.
2. Prior Art
Embodiments of the present invention provide improved devices for fluid control in various applications. A typical example is the control of a high pressure fuel injector. Typically, two-way poppet valves (open and closed) are used due to their superior leakage characteristics (low) and the ability to pressure balance a two-way poppet valve. It is highly desirable to use a three-way valve for improved performance and control, but this is difficult due to a three-way valve's inability to pressure balance completely unless it is a spool valve, which leaks excessively. For purposes of this disclosure, a three-way valve will be described as a valve coupling a supply (S) passage to a control (C) passage or coupling the control passage to a vent (V), though other port identifications may be more appropriate depending on the use of the three-way valve.
The choices for a three-way valve are:
Spool valve. A spool valve can create the required hydraulic paths, but while in either position (S-C or C-V) the valve has a very short leak (seal) path from a high-pressure area to a vented area, which can lead to high system parasitic losses. This valve can be designed to have a hydraulic short circuit (momentarily coupling of supply and vent when transitioning from one position to the other) or not, depending on the application. The advantages are primarily in its pressure balance, thereby requiring very low actuation forces, and in the ability to be designed to avoid the short circuit.
Three-way hard-seat valve (Poppet). This type of valve can have no leakage in either position, but when the valve is transitioning from one position to the other, there necessarily exists a direct flow path between the supply and the vent that could lead to large losses of energy and system noise. This type of valve cannot be completely pressure balanced, and therefore requires more actuating forces than a typical pressure balanced spool valve.
Two two-way hard-seat valves (Poppet). This option has no leakage and can have a direct flow path between the supply and the vent or not, depending on control of the system. The disadvantage of this system is that twice as many control valves are needed to achieve three-way control, adding system and control complexity, and further requires more room to package.
Thus the current choices and their disadvantages are:
Spool Valve: High static leakage.
Three-way hard-seat valve: High actuating force requirements (due to pressure imbalance) and short circuit loss.
Two, two-way hard seat valves: Cost and complexity.
Also known are three-way ball valves. Here a ball is moveable from one seat to an opposing seat, allowing fluid communication between a port at the side of the ball through whichever seat is uncovered by the ball. With the supply of pressure through one seat and the control at the side of the ball and the vent through the other seat, there is a momentary flow path between the supply and the vent during the transition of the ball from one seat to the other.